Methods and compositions for cementing pipe strings in well bores

ABSTRACT

The present invention provides improved methods and compositions for cementing pipe strings in well bores. The methods of the invention are basically comprised of preparing a cement composition comprised of a hydraulic cement, an epoxy resin, a hardening agent for the epoxy resin and sufficient water to form a pumpable slurry. Thereafter, the cement composition is introduced into the annulus between a pipe string and a well bore and the cement composition is allowed to set into a resilient impermeable solid mass.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to cementing subterranean wells,and more particularly, to cement compositions which set into resilientimpermeable solid masses and methods of using the compositions.

2. Description of the Prior Art

Hydraulic cement compositions are commonly utilized in primary cementingoperations whereby pipe strings such as casings and liners are cementedin well bores. In performing primary cementing, a hydraulic cementcomposition is pumped into the annular space between the walls of thewell bore and the exterior surfaces of the pipe string disposed therein.The cement composition is permitted to set in the annular space therebyforming an annular sheath of hardened substantially impermeable cementtherein. The cement sheath physically supports and positions the pipestring in the well bore and bonds the exterior surfaces of the pipestring to the walls of the well bore whereby the undesirable migrationof fluids between zones or formations penetrated by the well bore isprevented.

The cement compositions utilized in primary cementing must often belightweight to prevent excessive hydrostatic pressures from beingexerted on formations penetrated by well bores. A particularly suitabletechnique for making a hydraulic cement composition lightweight is tofoam the cement composition with a gas such as air or nitrogen. Inprimary cementing, a foamed cement composition provides the additionaladvantage of being compressible whereby formation fluids are less likelyto enter the annulus and flow through the cement composition thereinduring the transition time of the cement composition, i.e., the timeafter the placement of a cement composition in the annulus during whichthe cement composition changes from a true fluid to a hard set mass.

The development of wells including one or more laterals to increaseproduction has recently taken place. Such multi-lateral wells includevertical or deviated (including horizontal) principal well bores havingone or more ancillary laterally extending well bores connected thereto.Drilling and completion equipment has been developed which allowsmultiple laterals to be drilled from a principal cased and cemented wellbore. Each of the lateral well bores can include a liner cementedtherein which is tied into the principal well bore. The lateral wellbores can be vertical or deviated and can be drilled into predeterminedproducing formations or zones at any time in the productive life cycleof the well.

In both conventional single bore wells and multi-lateral wells havingseveral bores, the cement composition utilized for cementing casing orliners in the well bores must develop high bond strength after settingand also have sufficient resiliency, i.e., elasticity and ductility, toresist loss of pipe or formation bond, cracking and/or shattering as aresult of pipe movements, impacts and/or shocks subsequently generatedby drilling and other well operations. The bond loss, cracking and/orshattering of the set cement allows leakage of formation fluids throughat least portions of the well bore or bores which can be highlydetrimental.

The set cement in a well, and particularly the set cement forming acement sheath in the annulus between a pipe string and the walls of awell bore, often fails due to shear and compressional stresses exertedon the set cement. Such stress conditions are commonly the result ofrelatively high fluid pressures and/or temperatures inside the cementedpipe string during testing, perforating, fluid injection and/or fluidproduction. The high internal pipe pressure and/or temperature resultsin the expansion of the pipe string, both radially and longitudinally,which places stresses on the cement sheath causing it to crack or thecement bonds between the exterior surfaces of the pipe and/or the wellbore walls to fail whereby the loss of hydraulic seal in the annulusoccurs.

Another condition results from exceedingly high pressures which occurinside the cement sheath due to the thermal expansion of fluids trappedwithin the cement sheath. This condition often occurs as a result ofhigh temperature differentials created during the injection orproduction of high temperature fluids through the well bore, e.g., wellssubjected to steam recovery or the production of hot formation fluidsfrom high temperature formations. Typically, the pressure of the trappedfluids exceeds the collapse pressure of the cement and pipe causingleaks and bond failure.

Yet another compressional stress condition occurs as a result of outsideforces exerted on the cement sheath due to formation shifting,overburden pressures, subsidence and/or tectonic creep.

In multi-lateral wells wherein pipe strings have been cemented in wellbores using conventional well cement slurries which set into brittlesolid masses, the brittle set cement cannot withstand impacts and shockssubsequently generated by drilling and other well operations carried outin the multiple laterals without cracking or shattering.

The above described failures can result in loss of production,environmental pollution, hazardous rig operations and/or hazardousproduction operations. The most common hazard is the presence of gaspressure at the well head.

Thus, there are needs for improved well cement compositions and methodswhereby after setting, the cement compositions are highly resilient andcan withstand the above described stresses without failure. That is,there is a need for well cement compositions and methods whereby thecement compositions have improved mechanical properties includingelasticity and ductility and failures due to pipe movement, impacts andshocks are reduced or prevented.

SUMMARY OF THE INVENTION

The present invention provides improved methods of cementing pipestrings in well bores and improved cement compositions that upon settingform resilient solid masses which meet the needs described above andovercome the deficiencies of the prior art. The improved methods of theinvention are basically comprised of the steps of preparing an improvedcement composition of this invention, introducing the cement compositioninto the annulus between a pipe string and a well bore and allowing thecement composition to set into a resilient impermeable solid masstherein.

The improved compositions of this invention are basically comprised of ahydraulic cement, an epoxy resin, an epoxy resin hardening agent andsufficient water to form a pumpable slurry. The compositions can alsooptionally include amorphous silica powder, a dispersing agent, a setretarding agent and other suitable additives well known to those skilledin the art. Further, when required, the densities of the cementcompositions can be reduced by foaming the compositions, i.e., includinga gas, a foaming agent and a foam stabilizer in the compositions.

It is, therefore, a general object of the present invention to provideimproved methods of cementing pipe strings in well bores and improvedcement compositions which set into resilient impermeable solid masses.

Other and further objects, features and advantages of the presentinvention will be readily apparent to those skilled in the art upon areading of the description of preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides improved methods and compositions forcementing pipe strings in well bores. The cement compositions haveimproved resiliency without compromising strength or fatigue resistance.While the methods and compositions are useful in a variety of wellcompletion and remedial operations, they are particularly useful inprimary cementing, i.e., cementing casings and liners in well bores.

A non-foamed cement composition of this invention is basically comprisedof a hydraulic cement, an epoxy resin, a hardening agent for the epoxyresin and sufficient water to form a pumpable slurry. A variety ofhydraulic cements can be utilized in accordance with the presentinvention including those comprised of calcium, aluminum, silicon,oxygen and/or sulfur which set and harden by reaction with water. Suchhydraulic cements include Portland cements, pozzolana cements, gypsumcements, high aluminum content cements, silica cements and highalkalinity cements. Portland cements or their equivalents are generallypreferred for use in accordance with the present invention. Portlandcements of the types defined and described in API Specification ForMaterials And Testing For Well Cements, API Specification 10, 5thEdition, dated Jul. 1, 1990 of the American Petroleum Institute areparticularly suitable. Preferred API Portland cements include classes A,B, C, G and H, with API classes G and H being more preferred and class Gbeing the most preferred.

A variety of hardenable epoxy resins can be utilized in the cementcompositions of this invention. Preferred epoxy resins are thoseselected from the condensation products of epichlorohydrin and bisphenolA. A particularly suitable such resin is commercially available from theShell Chemical Company under the trade designation “EPON®RESIN 828.”This epoxy resin has a molecular weight of about 340 and a one gramequivalent of epoxide per about 180 to about 195 grams of resin. Anothersuitable epoxy resin is an epoxidized bisphenol A novolac resin whichhas a one gram equivalent of epoxide per about 205 grams of resin.

For ease of mixing, the epoxy resin utilized is preferably pre-dispersedin a non-ionic aqueous fluid. A non-ionic aqueous dispersion of theabove described condensation product of epichlorohydrin and bisphenol Ais commercially available from the Shell Chemical Company under thetrade designation “EPI-REZ®-3510-W-60.” Another non-ionic aqueousdispersion of an epoxy resin comprised of a condensation product ofepichlorohydrin and bisphenol A having a higher molecular weight thanthe above described resin is also commercially available from the ShellChemical Company under the trade designation “EPI-REZ®-3522-W-60.” Theabove mentioned epoxidized bisphenol A novolac resin is commerciallyavailable in a non-ionic aqueous dispersion from the Shell ChemicalCompany under the trade designation “EPI-REZ®-5003-W-55.” Of theforegoing non-ionic aqueous dispersions of epoxy resins, the aqueousdispersion of the condensation product of epichlorohydrin and bisphenolA having a molecular weight of about 340 and a one gram equivalent ofepoxide per about 180 to about 195 grams of resin is the most preferred.

The epoxy resin utilized is included in the compositions of thisinvention in an amount in the range of from about 5% to about 20% byweight of hydraulic cement in the composition, most preferably in anamount of about 8% to about 10%.

A variety of hardening agents, including, but not limited to, aliphaticamines, aliphatic tertiary amines, aromatic amines, cycloaliphaticamines, heterocyclic amines, amidoamines, polyamides, polyethyleneaminesand carboxylic acid anhydrides can be utilized in the compositions ofthis invention containing the above described epoxy resins. Of these,aliphatic amines, aromatic amines and carboxylic acid anhydrides are themost suitable.

Examples of aliphatic and aromatic amine hardening agents aretriethylenetetraamine, ethylenediamine, N-cocoalkyltri-methylenediamine,isophoronediamine, diethyltoluenediamine, and tris(dimethylaminomethylphenol). Examples of suitable carboxylic acidanhydrides are methyltetrahydrophthalic anhydride, hexahydrophthalicanhydride, maleic anhydride, polyazelaic polyanhydride and phthalicanhydride. Of these, triethylenetetraamine, ethylenediamine,N-cocoalkyltri-methylenediamine, isophoronediamine,diethyltoluenediamine and tris (dimethylaminomethylphenol) arepreferred, with isophoronediamine, diethyltoluenediamine andtris(dimethylaminomethylphenol) being the most preferred.

The hardening agent or agents utilized are generally included in thecement compositions of this invention in an amount in the range of fromabout 0.01% to about 0.02% by weight of hydraulic cement in thecompositions.

The water in the cement compositions which is in addition to the watercontained in the non-ionic aqueous dispersions of epoxy resin isincluded in the compositions to make the compositions pumpable. Thewater can be from any source provided it does not contain compounds thatadversely effect other components in the cement compositions. However,fresh water is preferred. Generally, water is present in thecompositions in an amount in the range of from about 20% to about 45% byweight of the hydraulic cement in the compositions, more preferably inthe range of from about 25% to about 30%.

Another component which can optionally be included in the cementcompositions of this invention is a set retarding agent. Set retardingagents are included in a cement composition when it is necessary toextend the time in which the cement composition can be pumped so that itwill not thicken or set prior to being placed in a desired location inthe well being cemented. Examples of set retarding agents which can beused include lignosulfonates such as calcium and sodium lignosulfonate,such lignosulfonates modified by reaction with formaldehyde and sodiumbisulfite, organic acids such as tartaric acid and gluconic acid, acopolymer or copolymer salt of 2-acrylamido-2-methyl propane sulfonicacid and acrylic acid and others. A particularly suitable set retardingagent for use in the cement compositions of the present invention iscalcium lignosulfonate modified by reaction with formaldehyde and sodiumbisulfite. This set retarding agent is commercially available under thetrade name “HR-6L™” from Halliburton Energy Services, Inc. of Duncan,Okla.

The proper amount of set retarding agent required for particularconditions can be determined by conducting a thickening time test forthe particular set retarding agent and cement composition. Such testsare described in the API Specification For Materials And Testing ForWell Cements, API Specification 10, mentioned above. Generally, the setretarding agent utilized is added to a cement composition of thisinvention in an amount in the range of from about 0.1% to about 3% byweight of hydraulic cement in the composition.

Other components which can optionally be included in the cementcompositions of this invention are amorphous silica powder and adispersing agent. The amorphous silica powder improves the compressivestrength and other mechanical properties of the cement composition andthe dispersing agent facilitates the dispersion of the amorphous silicapowder and other solids in the compositions.

Suitable amorphous silica powder which can be utilized is commerciallyavailable under the trade designation “SILICALITE™” from HalliburtonEnergy Services, Inc. of Duncan, Okla. While various dispersing agentscan be utilized, a particularly suitable such dispersing agent iscomprised of the condensation reaction product of formaldehyde, acetoneand sodium bisulfite. This dispersing agent is commercially availableunder the trade designation “CFR-3™” from Halliburton Energy Services,Inc. of Duncan, Okla.

When used, the amorphous silica powder is included in the cementcompositions of this invention in an amount in the range of from about10% to about 20% by weight of hydraulic cement in the compositions. Thedispersing agent used is included in the composition in an amount in therange of from about 0.05% to about 1% by weight of hydraulic cementtherein.

The above described non-foamed cement compositions of this invention canbe foamed by combining a compressible gas with the compositions in anamount sufficient to foam the compositions and produce a desired densityalong with an effective amount of a foaming agent and an effectiveamount of a foam stabilizer. As mentioned above, the presence of acompressible gas in the cement compositions helps prevent pressurizedformation fluid influx into the cement compositions while they aresetting and contributes to the resiliency of the set cementcompositions.

The gas utilized is preferably selected from nitrogen and air, withnitrogen being the most preferred. Generally, the gas is present in anamount sufficient to foam the cement compositions and produce a cementcomposition density in the range of from about 10 to about 16 pounds pergallon, more preferably from about 12 to about 14 pounds per gallon.

The foaming agent functions to facilitate foaming. Suitable foamingagents are surfactants having the general formula:

H (CH₂)_(a)(OC₂H₄)_(b)OSO₃X

wherein:

a is an integer in the range of from about 5 to about 15;

b is an integer in the range of from about 1 to about 10; and

X is any compatible cation.

A particularly preferred foaming agent of the above type is a surfactanthaving the formula:

H(CH₂)_(a)(OC₂H₄)₃OSO₃Na

wherein:

a is an integer in the range of from about 6 to about 10.

This surfactant is commercially available under the trade designation“CFA-S™” from Halliburton Energy Services, Inc. of Duncan, Okla.

Another particularly preferred foaming agent of the above mentioned typeis a surfactant having the formula:

H(CH₂)_(a)(OC₂H₄)_(b)OSO₃NH₄

wherein:

a is an integer in the range of from about 5 to about 15; and

b is an integer in the range of from about 1 to about 10.

This surfactant is commercially available under the trade name“HALLIBURTON FOAM ADDITIVE™” from Halliburton Energy Services, Inc. ofDuncan, Okla.

Another foaming agent which can be utilized in the cement compositionsof this invention includes polyethoxylated alcohols having the formula:

H(CH₂)_(a)(OC₂H₄)_(b)OH

wherein:

a is an integer in the range of from about 10 to about 18; and

b is an integer in the range of from about 6 to about 15.

This surfactant is available from Halliburton Energy Services under thetrade name “AQF-1™.”

Yet another foaming agent which can be used is a sodium salt ofalpha-olefinic sulfonic acid (AOS) which is a mixture of compounds ofthe formulas:

X[H(CH₂)_(n)—C═C—(CH₂)_(m)SO₃Na]

and

Y[H(CH₂)_(p)—COH—(CH₂)_(q)SO₃Na]

wherein:

n and m are individually integers in the range of from about 6 to about16;

p and q are individually integers in the range of from about 7 to about17; and

X and Y are fractions with the sum of X and Y being 1.

This foaming agent is available from Halliburton Energy Services underthe trade name “AQF-2™.”

Still another foaming surfactant which can be used is an alcohol ethersulfate of the formula:

H(CH₂)_(a)(OC₂H₄)_(b)SO₃NH₄

wherein:

a is an integer in the range of from about 6 to about 10; and

b is an integer in the range of from about 3 to about 10.

The particular foaming agent employed will depend on various factorssuch as the types of formations in which the foamed cement is tc beplaced. Generally, the foaming agent utilized is included in a cementcomposition of this invention in an amount in the range of from about1.5% to about 10% by weight of water in the composition. When thefoaming agent is one of the preferred surfactants described above, it isincluded in the composition in an amount in the range of from about 3%to about 5% by weight of water therein.

A foam stabilizer is also included in the foamed cement compositions toenhance the stability of the foam. One such foam stabilizing agent is acompound of the formula:

wherein:

R is hydrogen or a methyl radical; and

n is an integer in the range of from about 20 to about 200.

A particularly preferred foam stabilizing agent of the above type is amethoxypolyethylene glycol of the formula:

CH₃o(CH₂CH₂O)_(n)CH₂OH

wherein:

n is in the range of from about 100 to about 150.

This foam stabilizing agent is commercially available from HalliburtonEnergy Services under the trade designation “HALLIBURTON FOAMSTABILIZER™.”

The most preferred foam stabilizing agent is an amidopropylbetainehaving the formula:

R—CONHCH₂CH₂CH₂N⁺(CH₃)₂CH₂CO₂ ⁻

wherein:

R is a C₁₀ to C₁₈ saturated aliphatic hydrocarbon group, an oleyl groupor a linoleyl group.

A particularly suitable stabilizing agent of the above type is acocoylamidopropylbetaine. This foam stabilizing agent is commerciallyavailable from Halliburton Energy Services under the trade designation“HC-2™.”

The foam stabilizer is generally included in a cement composition ofthis invention in an amount in the range of from about 0.75% to about 5%by weight of water therein. When the foam stabilizing agent is one ofthe particularly preferred agents described above, it is preferablypresent in the composition in an amount in the range of from about 1.5%to about 2.5% by weight of water.

Thus, an improved well cement composition of this invention is comprisedof a hydraulic cement, an epoxy resin selected from the group of acondensation reaction product of epichlorohydrin and bisphenol A and anepoxidized bisphenol A novolac resin present in an amount in the rangeof from about 8% to about 10% by weight of hydraulic cement in thecomposition, a hardening agent for the epoxy resin selected from thegroup of aliphatic amines, aromatic amines and carboxylic acidanhydrides present in an amount in the range of from about 0.01% toabout 0.02% by weight of hydraulic cement in the composition, andsufficient water to form a pumpable slurry.

Another composition of the present invention is comprised of a hydrauliccement, an epoxy resin selected from the group of a condensationreaction product of epichlorohydrin and bisphenol A and an epoxidizedbisphenol A novolac resin present in an amount in the range of fromabout 8% to about 10% by weight of hydraulic cement in the composition,a hardening agent for the epoxy resin selected from the group ofaliphatic amines, aromatic amines and carboxylic acid anhydrides presentin the composition in an amount in the range of from about 0.01% toabout 0.02% by weight of hydraulic cement in the composition, a setretarding agent, e.g., an alkali metal or alkaline earth metallignosulfonate modified by reaction with formaldehyde and sodiumbisulfite, present in an amount in the range of from about 0.1% to about3% by weight of hydraulic cement in the composition, amorphous silicapowder present in an amount in the range of from about 10% to about 20%by weight of hydraulic cement in the composition, a dispersing agent,e.g., the condensation reaction product of formaldehyde, acetone andsodium bisulfite, present in an amount in the range of from about 0.05%to about 1% by weight of hydraulic cement in the composition andsufficient water to form a pumpable slurry.

Yet another composition of this invention is comprised of a hydrauliccement, an epoxy resin selected from the group of a condensationreaction product of epichlorohydrin and bisphenol A and an epoxidizedbisphenol A novolac resin present in an amount in the range of fromabout 8% to about 10% by weight of hydraulic cement in the composition,a hardening agent for said epoxy resin selected from the group ofaliphatic amines, aromatic amines and carboxylic acid anhydrides presentin an amount in the range of from about 0.01% to about 0.02% by weightof hydraulic cement in the composition, water present in an amount ofabout 25% to about 35% by weight of hydraulic cement in the composition,a gas present in an amount sufficient to form a foam having a density inthe range of from about 12 to about 14 pounds per gallon, a foamingagent, e.g., a sodium salt of alpha-olefinic sulfonic acid, present inan amount in the range of from about 3% to about 5% by weight of waterin the composition and a foam stabilizer, e.g.,cocoylamidopropylbetaine, present in an amount in the range of fromabout 1.5% to about 2.5% by weight of water in the composition.

Still another composition of this invention is comprised of a hydrauliccement, an epoxy resin selected from the group of a condensationreaction product of epichlorohydrin and bisphenol A and an epoxidizedbisphenol A novolac resin present in an amount in the range of fromabout 8% to about 10% by weight of hydraulic cement in the composition,a hardening agent for the epoxy resin selected from the group ofaliphatic amines, aromatic amines and carboxylic acid anhydrides presentin an amount in the range of from about 0.01% to about 0.02% by weightof hydraulic cement in the composition, water present in an amount inthe range of from about 25% to about 35% by weight of hydraulic cementin the composition, a set retarding agent, e.g., an alkali metal oralkaline earth metal lignosulfonate modified by reaction withformaldehyde and sodium bisulfite, present in an amount in the range offrom about 0.1% to about 3% by weight of hydraulic cement in thecomposition, amorphous silica powder present in an amount in the rangeof from about 10% to about 20% by weight of hydraulic cement in thecomposition, a dispersing agent, e.g., the condensation reaction productof formaldehyde, acetone and sodium bisulfite, present in an amount inthe range of from about 0.05% to about 1% by weight of hydraulic cementin the composition, a gas selected from the group of air and nitrogenpresent in an amount sufficient to foam the cement composition, aneffective amount of a foaming agent, e.g., the sodium salt of analpha-olefinic sulfonic acid, present in an amount in the range of fromabout 3% to about 5% by weight of water in the composition and a foamstabilizer, e.g., cocoylamidopropylbetaine, present in an amount in therange of from about 1.5% to about 2.5% by weight of water therein.

As mentioned, the improved methods of the present invention forcementing a pipe string in a well bore are basically comprised ofpreparing a cement composition of the present invention as describedabove, introducing the cement composition into the annulus between apipe string and a well bore and allowing the cement composition to setinto a resilient impermeable mass.

In order to further illustrate the methods and compositions of thisinvention, the following examples are given.

EXAMPLE 1

An unfoamed composition of the present invention having a density of16.4 pounds per gallon was prepared by mixing 720 grams of Premiumcement with 234.6 grams of water, 58.6 grams of a non-ionic aqueousdispersion of an epoxy resin and 0.9 grams of a hardening agent for theepoxy resin. The cement composition was divided into test samples andvarious quantities of a set retarding agent were added to some of thetest samples.

A second unfoamed cement composition of the invention having a densityof 16.4 pounds per gallon was prepared by combining 720 grams of Premiumcement with 252.8 grams of water, 0.5 grams of a dispersing agent and 80grams of amorphous silica powder. This cement slurry was also dividedinto test samples and a set retarding agent was added to some of thetest samples.

Foamed cement composition test samples were prepared by first mixing 720grams of premium cement with 234.6 grams of water, 58.6 grams of anaqueous dispersion of an epoxy resin and 0.9 grams of a hardening agent.This cement slurry having a density of 16.4 pounds per gallon wasdivided into test samples and a set retarding agent was added to some ofthe test samples. The test samples were then foamed to a density of 14pounds per gallon with air after combining a foaming agent, i.e., asodium salt of an alpha-olefinic sulfonic acid, in an amount of about1.67% by weight of water and a foam stabilizer, i.e., acocoylamidopropylbetaine, in an amount of 0.83% by weight of water withthe test samples.

Additional foamed cement composition test samples were prepared bymixing 720 grams of premium cement with 252.8 grams of water, 0.5 gramsof a dispersing agent and 80 grams of amorphous silica powder. Theresulting cement slurry having a density of 16.4 pounds per gallon wasdivided into test samples and various amounts of a set retarder wereadded to some of the test samples. The test samples were next foamedwith air to a density of 14 pounds per gallon after adding a foamingagent, i.e., a sodium salt of an alpha-olefinic sulfonic acid, to thetest samples in an amount of 1.67% by weight of water and a foamstabilizer, i.e., a cocoylamidopropylbetaine to the test samples in anamount of 0.83% by weight of water.

The test samples of the compositions of the present invention describedabove were tested for thickening times at 140° F. in accordance with theprocedures set forth in the API Specification 10 mentioned above. Thecomponents and their quantities in the various cement composition testsamples described above as well as the results of the thickening timetests are given in Table I below.

TABLE I Cement Composition Test Sample Components, Quantities andThickening Times Set Amorphous Cement Retarding Epoxy Epoxy HardeningDispersing Silica Thickening Composition Unfoamed Foamed Agent¹, %Resin², % Resin³, % Agent⁴, % Agent⁵, % Powder⁶, % Time @ Test SampleDensity, Density, by weight by weight by weight by weight by weight byweight of 140° F., No. lb/gal lb/gal of cement of cement of cement ofcement of cement cement Hr:Min 1 16.4 — 0.32 7.2 — 1.0 — — 3:05 2 16.4 —— — 7.2 0.86 — — 3:15 3 16.4 — 0.32 — 7.2 1.0 0.062 10 2:35 4 16.4 —0.10 — — — 0.062 10 — 5 16.4 — 0.10 — — — 0.062 — — 6 — 14 0.32 7.2 —1.0 — — 3:45 7 — 14 — — 7.2 0.86 — — 3:29 8 — 14 0.32 7.2 — 1.0 0.062 102:45 9 — 14 0.10 — 7.2 0.86 0.062 10 1:48 10 — 14 0.10 — — — 0.062 10 —11 — 14 0.10 — — — 0.062 — — ¹Calcium lignosulfate modified by reactionwith formaldehyde and sodium bisulfite. ²Non-ionic aqueous dispersion ofcondensate product of epichlorohydrin and bisphenol A (“Shell ChemicalEPI-REZ ® 3510-W-60”). ³Non-ionic aqueous dispersion of epoxidizedbisphenol A novolac resin (Shell Chemical “EPI-REZ ® 5003-W-55”).⁴Diethyltoluenediamine (Shell Chemical “EPI-CURE ® W”). ⁵Condensationproduct of formaldehyde, acetone and sodium bisulfite (Halliburton“CFR-3 ™”). ⁶Halliburton “Silicalite ™”

From Table I it can be seen that the thickening times of thecompositions of the present invention are within acceptable limits forcementing pipe strings in well bores.

The cement composition test samples described above were cured for 72hours at 140° F. Thereafter, Young's moduli, Poisson's ratios andcompressive strengths were determined under 0, 500, 1,000 and 2,000 psiconfining pressures. The cement composition test samples were alsotested for Brazilian tensile strengths and Mohr-Coulomb failureenvelopes were created. The results of these tests are set forth inTable II below.

TABLE II Medical Properties of Hardened Cement Composition Test SamplesCement Comp- Con- osition fining Com- Test Pres- pressive TensileYoung's Friction Sample sure, Strength, Strength, Modulus, Poisson'sAngle, No. psi psi psi 10⁶ psi Ratio degrees 1 0 9852 454 1.4 0.14 26.5500 8634 1.4 0.20 1000 9919 1.4 0.23 2000 11532 1.0 0.19 2 0 8524 4321.6 0.15 28 500 8247 1.3 0.20 1000 7696 0.74 0.14 2000 12557 1.1 0.16 30 8869 487 1.5 0.16 26 500 10047 1.4 0.13 1000 11584 1.4 0.21 2000 138961.4 0.27 4 0 8832 390 1.6 0.14 26.75 500 10258 1.2 0.24 1000 11958 1.30.19 2000 13258 0.93 0.20 5 0 8956 467 1.7 0.14 27 500 10401 1.5 0.291000 12166 1.6 0.28 2000 14419 1.4 0.23 6 0 2712 247 1.2 0.13 34 5004825 0.88 0.18 1000 4978 0.75 0.20 2000 9719 1.3 0.16 7 0 3122 286 1.00.13 12 500 3938 0.75 0.13 1000 5297 0.95 0.16 2000 6198 0.84 0.12 8 04669 262 0.87 0.13 14.5 500 5094 0.95 0.25 1000 6031 1.1 0.17 2000 78491.0 0.16 9 0 3922 234 0.87 0.14 8 500 4607 0.81 0.25 1000 5338 0.58 0.162000 6490 0.14 0.18 10  0 3833 343 1.0 0.15 24.5 500 5562 1.0 0.24 10006600 0.74 0.20 2000 8098 0.37 0.11 11  0 3088 290 0.75 0.13 21.1 5004074 0.78 0.23 1000 5440 0.86 0.21 2000 7364 0.72 0.18

As shown in Table II, unfoamed cement Composition Test Sample No. 3performed better than the other unfoamed test samples which includedepoxy resin and hardening agent. The compressive strengths were nearlythe same as unfoamed cement composition test samples 4 and 5 which didnot include epoxy resin and hardening agent (hereinafter referred to as“neat test samples”). The elastic properties of Test Sample No. 3 werelower, i.e., Test Sample No. 3 had an average Young's modulus of1.43×10⁶ psi versus an average Young's modulus of 1.53×10⁶ psi for aneat test sample, i.e., Test Sample No. 5. Poisson's ratio for the testsamples containing epoxy resin and hardening agent, i.e., Test SamplesNos. 1, 2 and 3 was an average of 0.18 which is significantly lower then0.24 for Test Sample No. 5. Test Sample No. 1 which is similar to TestSample No. 3 did not include amorphous silica powder and a dispersingagent. Test Sample No. 1 performed as well as Test Sample No. 3 at lowerconfinements, but had a somewhat lower strength at higher confinements.The other test samples containing epoxy resin and hardening agent (TestSample Nos. 2 and 3) showed similar Young's moduli and Poisson's ratioswhich means that the inclusion of epoxy resin and hardening agent in thecement composition imparts improved elasticity.

Poisson's ratio is a measure of a body's strain growth orthogonal to thedirection of applied stress. The results shown in Table II indicate thatthe cement compositions containing epoxy resin and hardening agent willhave better shear bonds with a pipe string because it will be lessflexible in lateral directions during loading of the pipe string.Tectonic creep and subsidence of rock formations cause increased stressloading and considerable displacement around the well bore. The lowerPoisson's ratios of the test samples including epoxy resin and hardeningagent indicate that the set cement compositions of this invention willmaintain their original shapes. The low Young's moduli indicate that thecement compositions will be more flexible in situations where there arelarge changes in loading. Another benefit is the apparent proclivity ofa number of the test samples including epoxy resin and hardening agenttowards high toughness, allowing a large amount of plastic creep.

As also shown in Table II, the angles of internal friction from theMohr-Coulomb shear failure envelopes are 20° to 30° which is in therange of more elastic rock. The angle of internal friction is often ameasure of a material's shear tendency. A steep angle is interpreted asa stiff, brittle material with high shear strength. The lower the angleof internal friction, the lower shear strength and less stable is thetested material under eccentric or changing compressive loads. Moderateangles of internal friction such as those observed for the variouscement compositions including epoxy resin and hardening agent shown inTable II indicate a more malleable, flexible material with reasonabletoughness. of the foamed cement composition test samples containingepoxy resin and hardening agent, Test Sample No. 8 (equivalent tounfoamed Test Sample No. 3) performed best. It was better than the neatTest Sample No. 11, but slightly weaker than the neat Test Sample No. 10which contained amorphous silica powder and dispersing agent. TheMohr-Coulomb failure envelope friction angles are also considered to beof high quality. Thus, the unfoamed and foamed cement compositions ofthis invention containing epoxy resin and hardening agent can withstanda variety of loading conditions. The cement compositions areparticularly suitable for cementing pipe strings in well bores and inmulti-lateral junctions which undergo rigorous cyclic loading, often inthe form of impacts and shocks. In addition, the resilient set cementcompositions of this invention have a better resistance to the effectsof drawdown and depletion of formations surrounding the well bore aswell as to subsidence and tectonic creep which often cause well borefailure and casing collapse.

Thus, the present invention is well adapted to carry out the objects andattain the ends and advantages mentioned as well as those which areinherent therein. While numerous changes may be made by those skilled inthe art, such changes are encompassed within the spirit of thisinvention as defined by the appended claims.

What is claimed is:
 1. An improved method of cementing a pipe string ina well bore comprising the steps of: (a) preparing a cement compositioncomprised of a hydraulic cement, an epoxy resin selected from the groupconsisting of a condensation reaction product of epichlorohydrin andbisphenol A and an epoxidized bisphenol A novolac resin, a hardeningagent for said epoxy resin, sufficient water to form a pumpable slurry,a gas, a foaming agent and a foam stabilizer; (b) introducing saidcement composition into the annulus between said pipe string and saidwell bore; and (c) allowing said cement composition to set into aresilient impermeable solid mass.
 2. The method of claim 1 wherein saidhydraulic cement in said composition is a Portland cement or theequivalent thereof.
 3. The method of claim 1 wherein said epoxy resin insaid composition is present in an amount in the range of from about 5%to about 20% by weight of hydraulic cement therein.
 4. The method ofclaim 1 wherein said hardening agent in said composition is at least onemember selected from the group of aliphatic amines, aromatic amines andcarboxylic acid anhydrides and is present in an amount in the range offrom about 0.01% to about 0.02% by weight of hydraulic cement therein.5. The method of claim 1 wherein said composition further comprises aset retarding agent present in an amount in the range of from about 0.1%to about 3% by weight of hydraulic cement therein.
 6. The method ofclaim 1 wherein said composition further comprises amorphous silicapowder present in an amount in the range of from about 10% to about 20%by weight of hydraulic cement therein.
 7. The method of claim 1 whereinsaid composition further comprises a dispersing agent present in anamount in the range of from about 0.05% to about 1% by weight ofhydraulic cement in said composition.
 8. The method of claim 1 whereinsaid gas in said composition is selected from the group of air andnitrogen and is present in said composition in an amount sufficient toproduce a composition density in the range of from about 10 to about 16pounds per gallon.
 9. The method of claim 1 wherein said foaming agentin said composition is selected from the group of foaming agentscomprised of the sodium salts of alpha-olefinic sulfonic acids andmixtures thereof and is present in an amount in the range of from about3% to about 5% by weight of water in said composition.
 10. The method ofclaim 1 wherein said foam stabilizer in said composition is selectedfrom the group of foam stabilizers having the formulaR—CONHCH₂CH₂CH₂N⁺(CH₃)₂CH₂CO₂ wherein R is a C₁₀-C₁₈ saturated aliphaticgroup, an oleyl group or a linoleyl group and is present in an amount inthe range of from about 1.5% to about 2.5% by weight of water in saidcomposition.